Microstructure evolution of SUS303 free-cutting steel during hot compression process

The hot-compression behavior and the microstructure evolution of SUS303 free-cutting steel were investigated in detail by carrying out compression tests in the temperature range of 1073–1323 K and at strain rates ranging from 0.01 to 30 s−1. From the true stress–true strain curves, dynamic recovery-type curve at low-temperature/high-strain rate and dynamic recrystallization-type curve at low-strain rate/high temperature were observed. During the low-temperature/low-strain rate hot-compression process, a large fraction of non-refined grains with large numbers of subgrains in their interiors were observed. These subgrains are thought to transform into new grains with further straining. During the high-temperature/low-strain rate hot compression process, discontinuous dynamic recrystallization was observed frequently. During the low-temperature/high-strain rate hot-compression process, only a few refined grains were observed near the grain boundaries, whereas at higher temperatures, a fully refined microstructure was obtained through an “explosive” static recrystallization during subsequent cooling process.